The present invention generally relates to Nyquist response restoring delta-sigma modulator data converters, more particularly relates to Nyquist response restoring delta-sigma modulator based analog-to-digital and digital-to-analog converters, and even more particularly relates to Nyquist response restoring delta-sigma modulator converters for use in radio frequency communication equipment. Further, the invention generally relates to high pass delta-sigma modulator data converters and more particularly relates to high pass delta-sigma modulator based analog-to-digital and digital-to-analog converters.
Digital (or xe2x80x9csoftwarexe2x80x9d) radios hold the promise of multiple-simultaneous-diverse signal transmission and reception over a wide bandwidth. The major components of such radios include direct sampling receivers (DSR) and direct digital transmitters (DDT). The wide bandwidth and the high dynamic range required for such radios have presented formidable obstacles to the development of this technology.
A DSR, for instance, can greatly reduce the conventional analog RF processing required of typical superheterodyne and homodyne receivers. This can lead to reduced cost, improved performance and multiple simultaneous signal recovery. The DSR""s analog-to-digital converter (ADC) must support very high spurious-free dynamic ranges, including suppressed distortion products.
Current wide bandwidth ADCs have less than 100 dB of dynamic range and suppressed distortion. The peak envelope power of a multi-signal RF environment, however, can require as much as 150 dB of dynamic range. This must be achieved by a combination of pre-analog-to-digital conversion, undesired signal peak-envelope-power reduction and a large ADC dynamic range. High dynamic range ADCs can be produced using delta-sigma modulators as long as the oversampling ratio is large (for example, 10 times oversampling for multi-bit and 100 times oversampling for single bit). However, the conversion of very wide (hundreds of megahertz) bandwidths, coupled with the high dynamic range, makes typical delta-sigma modulators impractical for use in a DSR.
In addition to the benefits listed above, DDTs can provide the added advantage of generating signals having extremely low noise and distortion. They also can have a reduced life cycle cost. Traditional transmitter technology has been basically limited to a single excitation signal (carrier). This is because the receiver""s sensitivity to low-level signals is likely compromised if the power amplifier is not extremely linear and low noise. This is especially true for co-site simultaneous transmit and receive applications. When the excitation contains multiple high level carriers, where there is probably a xe2x80x9cpicket fencexe2x80x9d of transmitted distortion products, this concern takes on added significance.
Generally, the only way to obtain the required linearity from active amplifiers is to use Class A power amplifier operation. This, however, results in low operating efficiency. It consequently becomes readily apparent that one signal per power amplifier uses less power to suppress the distortion products to an acceptable level. Further, high Q filters are of limited utility since the distortion products can lie close to the desired carriers.
Consequently, there exists a need for analog-to-digital and digital-to-analog modulator architectures capable of providing a wide bandwidth, spurious free dynamic range with suppressed distortion products. More specifically, there exists a need for multi-bit Nyquist response restoring delta-sigma modulator ADC and Power DAC (digital-to-analog) converters for use in direct sampling receiver and direct digital transmitter components. Further, there exists a need for a high pass delta-sigma modulator component suitable for use in the ADC and DAC architectures. There exists a need for architectures having the wide bandwidth performance of a Nyquist converter, the spurious free, high dynamic range of a delta-sigma modulator and substantially reduced or eliminated decimation and reconstruction filter requirements.
It is an object of the present invention to provide a high pass delta-sigma modulator for analog-to-digital and digital-to-analog converters, as well as digital resolution reducers.
It is a feature of the present invention to utilize a cascade of differentiators, a quantizer and a digital-to-analog converter feedback structure for high pass analog-to-digital converters.
It is a feature of the present invention to utilize a cascade of differentiators, a digital-to-analog transducer, and an analog-to-digital converter feedback structure for high pass digital-to-analog converters.
It is a feature of the present invention to utilize a cascade of differentiators, a digital resolution reducer and a digital resolution expander feedback structure for high pass digital resolution reducers.
It is an advantage of the present invention to enable the shifting of noise down in frequency from the pass band.
It is another object of the present invention to provide a multi-bit, Nyquist response restoring delta-sigma modulator analog-to-digital converter.
It is another feature of the present invention to utilize a delta-sigma modulator at the input.
It is another advantage of the present invention to provide a high resolution analog-to-digital converter having usable output bandwidth up to the Nyquist frequency (half the sample frequency) and to provide such at all frequencies simultaneously, without tuning.
It is yet another object of the present invention to provide a multi-bit delta-sigma modulator based, Power DAC using Nyquist response restored bandwidth processing.
It is yet another feature of the present invention to utilize a delta-sigma modulator structure at the input.
It is yet another advantage of the present invention to provide a high resolution digital-to-analog converter having usable output bandwidth up to the Nyquist frequency (half the sample frequency) and to provide such at all frequencies simultaneously, without tuning.
The present invention involves delta-sigma modulator architectures that are well suited for use as wide bandwidth, very high dynamic range ADCs and DACs. The present Nyquist response restored delta-sigma modulator invention is carried out in a manner such that the overall effective over sampling ratio approaches unity and does not require the high over sampling ratio of current delta-sigma ADCs. The underlying architectures utilize discrete time (or sample) integration and differentiation. In doing so, the modulators can exhibit much higher performance in multi-stage modulators than the popular continuous time (analog) integration and differentiation. As opposed to the continuous time modulators, the discrete time architectures have minimal phase shift at high frequencies (xc2xd sample clock). Using discrete time modulators allows for a high degree of control of the modulator transfer characteristics and their matching with the digital post processing. This permits the performance of specialized processing that would not be practical in typical delta-sigma modulators.
The Nyquist response restored delta-sigma modulator invention has several useful applications, including high performance RF conversion. For example, the present invention can be used as an ADC in a Direct Sampling Receiver, or as a linearized Power DAC in a Direct Digital Transmitter. When the present invention is used within a Direct Digital Transmitter or a Direct Sampling Receiver, it provides improved transmit signal generation or signal recovery performance, programmable flexibility and enables multiple-simultaneous-diverse-signal block transmission and recovery.